1. Field of the Invention
The present invention relates to routers for routing Internet Protocol (IP) packets and, more specifically, relates to routers and routing methods capable of transmitting packets according to a dynamic distribution ratio and responsive to a fault state in an output line.
2. Description of the Background
IP networks have gained explosive popularity in recent years, with the potential to substitute for telephone networks as one of the most important social infrastructures of society.
In order to reduce the cost of transmission line facilities, a procedure called Equal Cost Multipath is provided in an OSPF (Open Shortest Path First) protocol. The OSPF protocol increases the availability of the effective bandwidth allocated per virtual transmission channel by setting up redundant paths per channel, using a plurality of reduced cost lower-speed lines, and by distributing packets to the multiple lines. Descriptions of OSPF are given, for example, in RFC 2328.
In the OSPF procedure, if a plurality of paths exist and their costs (in terms of line speed, delay time, etc.) are equal when a router computes routing to a destination, the router sets these paths as the candidates for packet-forwarding paths in the routing table. If a plurality of packet-forwarding paths are set, when the router receives packets and determines a packet-forwarding path by searching the routing table, it selects one of the multiple paths according to a suitable distribution procedure. In this way, packets are load-distributed to a plurality of paths, and the multiple paths are regarded as one virtual transmission channel. Utilizing this method, an increase in the availability of effective transmission channel bandwidth can be realized with reduced cost.
Procedures for enabling a quick recovery from a network fault, for example, Automatic Protection Switch (APS), are known. In the APS, as the substitute for a normally operating communication path (working path), an additional communication path (backup path) is prepared in advance to be used in the event that a fault occurs in the working path. While the working path is normally used to forward data, in addition to the data forwarded by the working path, some data (referred to herein as “surplus data”) can be forwarded by using the backup path. When a fault occurs, path switchover is performed in order to use the backup path to forward data that has been forwarded by the working path. Because of the backup path setup in advance and the definite correspondence between the working and backup paths, switchover processing in the event of a fault occurring is simple, and rapid path switchover can be performed.
In the Equal Cost Multipath procedure, a packet-distributing procedure is determined (whether or not the packets are distributed to multiple paths, the number of paths to be used for distributing the packets, and others) in accordance with the destination of the packets, but distributing packets in accordance with their priority cannot be performed.
On the other hand, in the APS, no consideration is given to the protection of high-priority packets at the switchover from the working path to the backup path.